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To achieve the full utilization of waste rice noodle (WRN) without secondary pollution, activated carbon (AC) and carbon quantum dots/titanium dioxide (CQDs/TiO2) composite were simultaneously synthesized by using WRN as raw material. Both of the two materials showed potential applications in water pollution control. The AC based on WRN displayed a porous spherical micro-morphology, which could absorb heavy metal elements like Pb(II) and Cr(VI) efficiently, with a maximum equilibrium uptake of 12.08 mg·g−1 for Pb(II) and 9.36 mg·g−1 for Cr(VI), respectively. The adsorption of the resulted AC could match the Freundlich adsorption isotherm and the pseudo-second-order kinetics mode. On the other hand, the CQDs/TiO2 composite based on WRN displayed a high efficient photocatalytic degradation effect on various water-soluble dyes such as methylene blue, malachite green, methyl violet, basic fuchsin, and rhodamine B under visible light irradiation, which showed better photocatalytic performance than commercial TiO2. The introduction of CQDs based on WRN to TiO2 could result in efficient electron-hole pair separation and enable more photogenerated electrons to reduce O2 and more photogenerated holes to oxidize H2O or OH−, which could cause stronger abilities in producing O2·− and ·OH radical and better photocatalytic activity.

Abstract Satellite altimetry is the main tool for constructing global or regional marine gravity fields. To improve the accuracy and spatial resolution, it is necessary to fuse multi-mission altimeters. How to determine the weights of multi-mission altimeters is a crucial issue, making the conventional calculation process very complex. In addition, traditional satellite inversion methods are often independent of shipborne gravity, which is used only as validation data, thus not take full advantages of high accuracy and resolution of shipborne gravity. In this study, we introduce a convolutional neural network (CNN) to merge the vertical deflections (DOVs) obtained from multi-altimeter missions to construct a marine gravity model in the South China Sea. High-accuracy shipborne gravity and a dataset comprising DOVs and geo-locations are employed as input data for neural network training. For the validation of CNN method, the gravity model is also computed by conventional Inverse Vening Meinesz (IVM) method. Independent shipborne gravity measurements and SIO V32.1, DTU17 models are used as validation data. The evaluation results show that the CNN-derived model achieves a higher level of accuracy, yielding a standard deviation (STD) of 3.21 mGal, with an improvement of 36.56% compared to IVM-derived model. More than 92% of the differences between the CNN-derived model and shipborne gravity are less than 5 mGal. In addition, spectral analysis results further show that the CNN-derived model has stronger energy at short wavelengths (less than 25 km) compared to other models. These findings reveal that CNN method is feasible for marine gravity recovery and the CNN-derived model can achieve higher accuracy. The CNN method can improve the accuracy and spectral characteristics of the constructed gravity model by taking advantage of the high accuracy and high resolution of shipborne gravity. Graphical Abstract

The deflection of the vertical (DOV) is the key information in the study of ocean gravity field. However, in most areas, the precision of the prime component of DOV is significantly lower than that of the meridian component. To obtain higher accuracy and resolution of ocean gravity information, researchers have proposed a novel altimeter called the wide-swath altimeter. This altimeter allows for the simultaneous acquisition of high-precision and high-resolution two-dimensional measurements of sea surface height (SSH). In this paper, the Surface Water and Ocean Topography (SWOT) mission with a wide-swath altimeter on board is selected for research. One cycle of SWOT sea surface height data is simulated to inverse the DOV in the Arabian Sea (45°E—80°E, 0°–30°N), and the inversion results are compared with those of conventional altimeter data. The results demonstrate that the difference between the meridian and prime components derived from the inversion of SWOT wide-swath data is minimal, significantly outperforming the inversion results of conventional nadir altimeter data. The advantage of SWOT wide-swath altimeter lies in its ability to use the multi-directional geoid slope at any sea surface measurement point to invert the components in the meridian and prime directions. To investigate the impact of this advantage on inversion precision, this paper employs a method to calculate the gradient of the geoid in multiple directions to invert DOV components. The improvement effect of calculating the gradient of the geoid in multiple directions on the precision of DOV component is analyzed. It is found that the accuracy of DOV inversion has significantly improved with the increase of geodetic gradient calculation direction. In addition, the effects of various errors and grid spacing in SWOT wide sea surface height data on the precision of DOV inversion are also analyzed.

It is commonly believed that the atmosphere is decoupled from the solid Earth. Thus, it is difficult for the seismic wave energy inside the Earth to propagate into the atmosphere, and atmospheric pressure wave signals excited by earthquakes are unlikely to exist in atmospheric observations. An increasing number of studies have shown that earthquakes, volcanoes, and tsunamis can perturb the Earth's atmosphere due to various coupling effects. However, the observations mainly focus on acoustic waves with periods of less than 10 min and inertial gravity waves with periods of greater than 1 h. There are almost no clear observations of gravity waves that coincide with observations of low-frequency signals of the Earth's free oscillation frequency band within 1 h. This paper investigates atmospheric gravity wave signals within 1 h of surface-atmosphere observations using the periodogram method based on seismometer and microbarometer observations from the global seismic network before and after the July 29, 2021 MW8.2 Alaska earthquake in the United States. The numerical results show that the atmospheric gravity wave signals with frequencies similar to those of the Earth's free oscillations 0S2 and 0T2 can be detected in the microbarometer observations. The results confirm the existence of atmospheric gravity waves, indicating that the atmosphere and the solid Earth are not decoupled within this frequency band and that seismic wave energy excited by earthquakes can propagate from the interior of the Earth to the atmosphere and enhance the atmospheric gravity wave signals within 1 h.

We propose a method for enhancing the accuracy of bathymetry models based on a multilayer perceptron (MLP) neural network that integrates the differences in multisource marine geodetic data (MMGD) (longitude, latitude, reference bathymetry, slope, the meridional and prime components of vertical deflection, gravity anomaly, vertical gravity gradient, and mean dynamic topography). First, we use the MMGD differences between the shipborne sounding control points within 8′ × 8′ grid points and shipborne sounding control points as input data, as well as the differences between the topo_24.1 model and the measured bathymetric values at the control points as output data to train the MLP model. Second, we feed the input data from the central point of a 1′ × 1′ grid into the MLP model to obtain predictions, and then use the topo_24.1 model to recover the predicted bathymetry at the prediction point. We focus on the Caribbean Sea, and construct a Caribbean Bathymetric Chart of the Oceans (CBCO1) model using MLP neural network. The reliability of MMGD, a CBCO2 model using MMGD, and the reliability and effectiveness of the overall method are demonstrated through comparisons with the CBCO2, GEBCO_2022, topo_24.1, DTU18 models at the checkpoints.

The orthometric height variation is evident through changes in the geoid and surface vertical displacements. Hydrological mass change can induce variations in geoid height and surface deformation, consequently resulting in fluctuations in orthometric height. Studying the orthometric height variations in the Mississippi River Basin (MRB) caused by surface mass changes is crucial for understanding crustal uplift and ecological evolution. In this study, the superiority of daily solutions was demonstrated through comparison with the monthly solutions. Based on the spherical harmonic function (SHF) and Green's function (GF) methods, the orthometric height variations in the MRB were calculated by utilizing daily ITSG-Grace2018 solutions and a hydrological model. These results were then compared with the daily solutions obtained from 26 global positioning system (GPS) stations within the study area. The results show that the spatial distribution of orthometric height variations in the MRB is uneven. Except for the western mountainous areas, which show an upward trend, the main trend is a decrease at a rate of 0.1–0.4 mm/yr. The average correlation coefficient between GPS solutions and the orthometric height variations calculated using SHF and GF is 0.71 and 0.72, respectively, indicating good consistency, and hydrological loading was identified as a significant factor contributing to the orthometric height variations. After correcting GPS solutions with global land data assimilation system (GLDAS), vertical tectonic motion rates were calculated at GPS stations. With the exception of a few GPS stations that were uplifted, most of the remaining GPS stations settled at a rate of 0.5–2.6 mm/yr.

Abstract The East China Sea, situated at the intersection of the Eurasian, Philippine Sea, and Pacific plates, is characterized by complex geology influenced by tectonic phenomena such as plate movements, volcanism, faults, and uplifts. Crustal density structure inversion provides a thorough understanding of the region's geological history as well as Earth's dynamical evolution, providing critical insights into seismic disaster mitigation, resource exploration, marine environmental protection, and maritime safety. The inversion process, on the other hand, presents challenges in data quality, quantity, model complexity, uncertainty, and computational resources. With the advancement of next-generation satellite gravity measurements and developing inversion techniques, the inversion of marine crustal density structures promises to be more precise and comprehensive. We explored the density distribution in the East China Sea and surrounding areas using an innovative wavenumber domain three-dimensional density imaging method along with high-precision global satellite gravity data. By overcoming data quality and computing resource constraints, wavenumber domain three-dimensional density imaging has transformed the discipline of marine geophysics, successfully delivering accurate density distributions in the study area. We were able to get a more precise and comprehensive characterization of the crustal density structure by combining high-precision satellite gravity data and cutting-edge imaging methods. Our investigation has unveiled previously unknown details about density distribution in the East China Sea and its environs. The East China Sea shelf displays smooth low-density perturbations at 18 km depth, whereas the trench–arc–basin region exhibits increasing density perturbations. Notably, the Okinawa Trough, which is surrounded by the Tokara Volcanic Ridge and the Ryukyu Trench, displays strong positive anomalies with a north–northeastern to northeastern orientation. In contrast, the Ryukyu Ridge and the Philippine Sea Basin exhibit smaller negative values and substantial northwestward positive density trends, respectively. These findings indicate diverse material distribution, which provides important insights into the area’s geological evolution and tectonic processes. This study adds new insights into density distribution in the East China Sea and adjacent regions, offering information on the geological complexity of the region. The research lays the groundwork for future research on crustal dynamics and enhances the field of marine geophysics and related disciplines. Graphical abstract

Abstract Given the spatial resolution of ~300 km in Gravity Recovery and Climate Experiment (GRACE) measurements, accurately quantifying mass variations at smaller scales proves challenging. Here, we present a high-resolution time-variable gravity field model of continental North China. This model, denoted as IGP-NorthChina2022TG, contains 15 gravity field solutions determined using an innovative approach that relies on terrestrial gravity measurements and Slepian basis functions. IGP-NorthChina2022TG provides degree 150 gravity changes (spatial resolution of ~120 km) on a semi-annual basis from September 2009 to September 2016, in contrast to the monthly degree 60 GRACE solutions. Despite their different temporal resolutions, the good agreement between GRACE and the ground-based results up to degree 60 confirms the robustness and reliability of the proposed method and favors the combination of these two types of measurements. The gravity changes with much finer spatial resolution from IGP-NorthChina2022TG could complement GRACE solutions for sub-regional scale investigations in North China.

Abstract The precise prediction of polar motion parameters is needed for the astrogeodynamics, navigation and positioning of the deep space probe. However, the current prediction methods are limited to predicting polar motion for specific periods, either short- or long-term. In this study, a sliding multilayer perceptron (MLP) method combined singular spectrum analysis (SSA) and autoregressive moving average (ARMA) for short- and long-term polar motion prediction was proposed. MLP was introduced into PM prediction due to its automatic learning characteristics and its ability to effectively process nonlinear and multi-dimensional data. The SSA was used to extract and predict the principal components of polar motion, while the remaining components were predicted using ARMA. In the meantime, SSA and ARMA were used to provide training data and target learning data for the MLP model. MLP input data were constructed by sliding processing with a window of 7 days, composed of n series of the same length (18 years). Finally, MLP was employed to predict the residuals generated during SSA and ARMA prediction. To evaluate the accuracy of the proposed method, the polar motion prediction was applied for a 364-day lead time based on the IERS EOP 14C04 product. The method outperformed the IERS Bulletin A, as demonstrated by the mean-absolute errors of the x and y components of polar motion on the 30th day, which were lower (5.14 mas and 3.37 mas, respectively) than those predicted by IERS Bulletin A (6.66 mas and 3.94 mas). Similarly, the mean-absolute errors on the 364th day were 17.79 mas and 16.29 mas, respectively, compared to the 19.24 mas and 18.81 mas predicted by IERS Bulletin A. Graphical Abstract

Gravity field is the most basic physical field generated by the material properties of the Earth system. It reflects the spatial distribution, movement and change of materials determined by the interaction and dynamic process inside the Earth. Over the years, a variety of technical means have been used to detect the Earth’s gravity field and supported numerous studies on the global change, resource detection, geological structure movement, water resources change and other related fields of research. Here is part of the progress in surface and marine gravimetry obtained by Chinese geodesy scientists from 2019 to 2023 from the following aspects, including: ① Continuous gravity network in Chinese mainland; ② Application of superconducting gravity measurement; ③ Network adjustment for continental-scale gravity survey campaign and data quality control; ④ Regional time-variable gravity field and its application; ⑤ Research progress on novel technologies for gravity inversion; ⑥ Research progress on marine gravity field determination; ⑦ Application research on marine gravity field.

The Tibetan Plateau (TP) is the youngest orogenic belt resulting from a continental collision on the Earth. It is a natural laboratory for studying continental dynamics, such as continental convergence, plate subduction, and plateau uplift. Investigating the deep structure of the TP has always been a popular issue in geological research. The Moho is the boundary between the crust and the mantle and therefore plays a crucial role in the Earth’s structure. Parameters such as depth and lateral variation, as well as the fine structure of the crust–mantle interface, reveal the lithospheric dynamics in the TP. Two methods are generally employed to study the Moho surface: seismic detection and gravity inversion. Seismic detection has the characteristic of high precision, but it is limited to a few cross-sectional lines and is quite costly. It is not suitable for and cannot be carried out over a large area of the TP. The Moho depth over a large area can be obtained through gravity inversion, but this method is affected by the nature of gravity data, and the accuracy of the inversion method is lower than that of seismic detection. In this work, a high-precision gravity field model was selected. The Parker–Oldenburg interface inversion method was used, within the constraints of seismic observations, and the Bott iteration method was introduced to enhance the inversion efficiency. The Moho depth in the TP was obtained with high precision, consistent with the seismic detection results. The research results showed that the shape of the Moho in the TP is complex and the variation range is large, reaching 60−80 km. In contrast with the adjacent area, a clear zone of sharp variation appears at the edge of the plateau. In the interior of the TP, the buried depth of the Moho is characterized by two depressions and two uplifts. To the south of the Yarlung Zangbo River, the Moho inclines to the north, and to the north, the Moho depresses downward, which was interpreted as the Indian plate subducting to the north below Tibet. The Moho depression on the north side of the Qiangtang block, reaching 72 km deep, may be a result of the southward subduction of the lithosphere. The Moho uplift of the Qiangtang block has the same strike as the Bangong−Nujiang suture zone, which may indicate that the area is compensated by a low-density and low-velocity mantle.

Earthquake prediction remains a challenging and difficult task for scientists all over the world. The tidal triggering of earthquakes is being proven by an increasing number of investigations, most of which have shown that earthquakes are positively correlated with tides, and thus, tides provide a potential tool for earthquake prediction, especially for imminent earthquakes. In this study, publications concerning the tidal triggering of earthquakes were compiled and analyzed with regard to global earthquakes, which were classified into three main types: tectonic, volcanic, and slow earthquakes. The results reveal a high correlation between tectonic earthquakes and tides (mainly for semidiurnal and diurnal tides; 14-day tides) before and after the occurrence of significant earthquakes. For volcanic earthquakes, observations of volcanoes on the seafloor and land indicate that volcanic earthquakes in near-shore volcanic areas and mid-ocean ridges have a strong correlation with tidal forces, mostly those with semidiurnal and diurnal periods. For slow earthquakes, the periodicity of the tremor duration is highly correlated with semidiurnal and diurnal tides. In conclusion, the tidal triggering of these three types of earthquakes makes a positive contribution to earthquake preparation and understanding the triggering mechanism, and thus, the prediction of these types of earthquakes should be investigated. However, there are still several inadequacies on this topic that need to be resolved to gain a definitiveanswer regarding the tidal triggering of all earthquakes. The main inadequacies are discussed in this paper from our point of view.

Modern geodetic technologies such as high-precision ground gravity measurements, satellite gravity measurements, the global navigation satellite system, remote sensing methods, etc. provide rich observation data for monitoring various geodynamic processes of the global Earth and its surface. The 19th International Symposium on Geodynamics and Earth Tides brought together scientific researchers from 26 countries around the world, shared the application of various measurements in different geoscience issues, covering Earth tidal deformation, oceanic and atmospheric loading effects, earthquake cycle, hydrology, Earth rotation changes, etc., and provided a precious exchange platform for global peers.

As a major grain-producing region in China, the North China Plain (NCP) faces serious challenges such as water shortage and land subsidence. In late 2014, the Central Route of the South-to-North Water Diversion Project (SNWD-C) began to provide NCP with water resources. However, the effectiveness of this supply in mitigating land subsidence remains a pivotal and yet unassessed aspect. In this paper, we utilized various geodetic datasets, including the Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow On (GRACE-FO), Global Navigation Satellite System (GNSS) and leveling data, to conduct a spatial-temporal analysis of the equivalent water height (EWH) and vertical ground movement in the NCP. The results reveal a noteworthy decline in EWH from 2011 to 2015, followed by a slight increase with minor fluctuations from 2015 to 2020, demonstrating a strong correlation with the water resources supplied by the SNWD-C. The GRACE-derived surface deformation rate induced by hydrological loading is estimated to be

The tidal Love numbers of the Moon are a set of nondimensional parameters that describe the deformation responses of the Moon to the tidal forces of external celestial bodies. They play an important role in the theoretical calculation of the Moon’s tidal deformation and the inversion of its internal structure. In this study, we introduce the basic theory for the theoretical calculation of the tidal Love numbers and propose a new method of solving the tidal Love numbers: the spectral element method. Moreover, we explain the mathematical theory and advantages of this method. On the basis of this new method, using 10 published lunar internal structure reference models, the lunar surface and lunar internal tidal Love numbers were calculated, and the influence of different lunar models on the calculated Love numbers was analyzed. Results of the calculation showed that the difference in the second-degree lunar surface Love numbers among different lunar models was within 8.5%, the influence on the maximum vertical displacement on the lunar surface could reach ±8.5 mm, and the influence on the maximum gravity change could reach ±6 μGal. Regarding the influence on the Love numbers inside the Moon, different lunar models had a greater impact on the Love numbers h2 and l2 than on k2 in the lower lunar mantle and core.

Abstract The western segment of the suture zone between the Yangtze and Cathaysia blocks, which is the most important tectonic boundary related to the formation and rifting of south China, is enigmatic and not fully understood due to the sporadic exposure of Precambrian strata and ophiolites. Three‐dimensional electrical resistivity models derived from inversion of magnetotelluric data identified a lithospheric‐scale conductive zone extending northeastwards beneath the Youjiang basin, which was interpreted as the western segment of the suture zone. The high conductivity and coincident high magnetic anomalies closely match the location of Carlin‐type gold deposits, which can be explained by fluids and gold‐bearing sulfide minerals in a fossil suture zone. Inconsistent with the southeast‐dip resolved at the eastern segment of the suture zone (the Jiangshan‐Shaoxing fault) in the earlier study, the slightly north‐dipping geometry at the western suture zone implies the reactivation by northward subduction and closure of the Paleo‐Tethys Ocean.

Traditional bathymetry inversion methods that rely on an altimetry-derived gravity anomaly (GA) and/or a vertical gravity gradient anomaly (VGG) have been widely used for bathymetry prediction in the South China Sea. However, few studies attempt new methods to combine multisource gravity data to improve the accuracy of the bathymetry. In this study, we introduce a fully connected deep neural network (FC-DNN) to merge GA, VGG, and the deflection of vertical (DOV) to predict the bathymetry in the South China Sea. Single beam sounding depths were used as sample data for neural network training. Independent shipboard depths and GEBCO2023, topo_25.1, and ETOPO2022 models were applied as validation data. The assessment results showed that the FC-DNN model reached a high precision level with an STD of 49.20 m. More than 70% of the differences between the FC-DNN bathymetric model and other depth models were less than 100 m. Furthermore, the spectral analysis results showed that the FC-DNN bathymetry model has stronger energy in medium and short wavelengths than other models, which indicates that additional gravity field element DOVs can recover richer topographic signals in those particular bands.

Earthquakes perturb both the ocean bottom topography due to displacements of sea floor and the geoid due to mass redistribution, which induces the relative sea level (RSL) change. However, the relative global mean sea level (GMSL) change is zero in that sea water mass is conserved. But the absolute GMSL change is not zero because earthquakes displace total ocean mass with respect to the Earth's center of mass (CM) which remains unchanged after an earthquake. This displacement, i.e. the absolute GMSL change, may be detectable by altimetry since the satellites are orbiting around CM. In this paper, we proposed a method to estimate co-seismic absolute GMSL change caused by earthquakes based on the point dislocation theory for a spherically symmetric, non-rotating, elastic and isotropic (SNREI) Earth. This change can be directly connected to the perturbation of ocean bottom topography. We first computed co-seismic displacements as well as the change in geo-potential and solved the sea level equation to validate the insignificance of the oceans' feedback, i.e. the loading effect due to RSL change, to co-seismic displacements. The results imply that the loading effect due to RSL change is negligible on displacements while is considerable on geoid. We then computed the absolute GMSL change caused by co-seismic vertical and horizontal displacements by making use of the integrated Green's function method. The numerical results show that a large earthquake may raise the absolute GMSL by magnitude of sub-millimeter and the recent three large events cause GMSL to rise about one millimeter, in which the contribution from horizontal displacement is non-negligible. Keywords: Point dislocation theory, SNREI earth, Sea level equation, Absolute GMSL, Ocean bottom topography

Background free oscillations (BFOs), observed even during seismically quiet periods, have been widely recognized. Although atmospheric or/and oceanic disturbances are suggested to be the possible excitation sources, there still exist some unknown uncertainties regarding their contribution. Note that most studies used seismometer records to explore the excitation mechanism of BFOs, while only a few used superconducting gravimeter (SG) records just for detection purposes. In view of the high precision, the wide measurement range and the increase of SGs distributed worldwide, this paper aims to further explore the excitation mechanism of BFOs by combining recent gravity records at several low-noise SG stations, rather than traditional seismometer records. We first analyzed gravity records at each station to ensure the detection of BFOs from spectrograms and averaged power spectra. On the basis of the BFOs detection, annual variations of the modal energy in the averaged spectrograms stacked over all stations and over different years were calculated. By comparing them with those derived from atmospheric/oceanic observations, we proved qualitatively that the atmospheric disturbance is the major excitation source of BFOs while the oceanic disturbance plays a relatively minor role below 5 mHz for the whole period considered; however, the excitation of BFOs could be mainly attributed to the oceanic disturbance for a certain period. It is necessary to further quantitatively estimate the modal energy excited by these disturbances, but as a supplementary means of seismic exploration, the results in this paper are expected to be helpful for understanding BFOs.

We accurately retrieved tidal gravimetric parameters using long-term continuous tidal gravity measurements recorded by superconducting gravimeters (SGs) at stations in Lhasa, Lijiang, and Wuhan, China. We used these results to investigate the influences of the special tectonic setting on regional tidal deformation. We accurately evaluated scale factors of SGs with high precision better than 0.06%. We carefully removed the effects of barometric pressure and oceanic loading from tidal gravity observations. We did not observe any obvious differences in amplitude factors for main tidal gravity waves for the stations in Lhasa and Lijiang. In the plateau area, we found the amplitude factor to be about 0.34% larger than that in the plain (Wuhan). Our study shows for the first time that the main reason for such tidal gravity anomalies can be explained by the influence of the special tectonic setting in the Tibetan Plateau.

Abstract In order to verify the time variability of free core nutation (FCN) period, global superconducting gravimeter (SG) observations were analyzed based on synthetic test data. The gravity data series were synthesized to check the detectability of resonance variation caused by FCN period change. The tests indicate that the discrepancy between the FCN periods determined by SG and VLBI observations is caused by the high correlation between the FCN parameter and the amplitude factor of the ψ1 wave. The K1 wave is more sensitive to the FCN period change than other diurnal waves. The limit of the standard deviation of the K1 wave is found for more precisely observing the FCN period change. Tidal parameters of diurnal waves estimated from long series of 20 global SG stations were analyzed. A common variation trend is found in the amplitude factor of both K1 and ψ1 waves in all 8 stations above the limit, which indicates the FCN period may be not so stable in time. Furthermore, the variation in the K1 and ψ1 waves constrains the FCN period change to between 2.5 and 4 sidereal days, which also agrees with the possible variation from the current VLBI and SG observations.